Digital programming of various functions such as industrial processes or resistance heating of conventional electric stoves is known. However, such devices do not have the same fail-safe requirements as microwave cookers. For example, prevention of excess electromagnetic radiation is a problem with conventional electric stoves and, hence, conventional digitally controlled sequences of control circuits may be used.
Microwave cookers, however, for example of the type shown in copending application Ser. No. 479,379 filed June 14, 1974 by Richard A. Foerstner, required that a frozen or partially frozen food body be cooked with a time sequence. A timer is manually reset a number of times to apply the microwave energy and to then allow the food body to set for a period to transfer heat by conduction to those portions of the food body which absorb less microwave energy due, for example, to having ice crystals formed therein which have a lower loss at the microwave frequency of 2.45 KMH predominantly used for microwave cooking. Attempts to avoid the necessity for manually resetting the timer at the end of each application of defrosting microwave energy have been tried, for example, by providing additional mechanical timers which are interconnected by additional relay contacts to produce various sequences of operation, but such devices have proved expensive and have required additional switch contacts which can be a source of maintenance.